The present invention relates to a room temperature-curable polyoxyalkylene polyether composition or, more particularly, to a polyoxyalkylene polyether composition curable at room temperature into a rubbery elastomer in the presence of moisture.
In the prior art, there are known curable compositions of which the base component is a polyoxyalkylene polyether having hydrolyzable groups, e.g. alkoxy, acyloxy, ketoximato and amino groups, at both chain ends introduced by modifying with organosilyl groups with the hydrolyzable groups bonded thereto (see, for example, Japanese Patent Disclosure No. 52-73998). These polyoxyalkylene polyethers are stable when kept in a neutral and anhydrous condition but, due to the presence of the hydrolyzable groups at the chain ends, they are defective in their instability that they are subject to the hydrolysis condensation reaction in the presence of moisture so that they must be handled in a dry condition and that their viscosity or consistency is readily increased leading to eventual gelation when kept in contact with a filler with basicity or acidity acting as a catalyst so that the formulation of a room temperature-curable composition on the base thereof is limited. In addition, a sufficiently high curing velocity of such a composition is obtained only by the addition of a considerable amount of a tin- or titanium-containing curing accelerator with consequent decrease not only in the heat resistance but also in the weathering resistance of the cured product thereof to a great extent.
Turning now to the discussion of the curing mechanism of such curable compositions, they are classified by the nature of the condensation reaction resulting in the formation of crosslinks. For example, the condensation product produced by the reaction may be a carboxylic acid, an amine, an oxime or an alcohol. The condensation reaction which proceeds with formation of a carboxylic acid, amine or oxime is disadvantageous because the carboxylic acid, amine and oxime are mostly a gaseous product with unpleasant odor having toxicity or corrosiveness so that compositions of such kinds can be used only under sufficiently strong ventilation and, when they are applied to a metal surface, treatment of the metal surface in advance with a primer is indispensable.
On the other hand, a curable composition in which the cross-links are formed by the dealcoholation condensation is almost free from the problems of toxicity and corrosiveness whereas such a composition is defective in the relatively low storage stability and rather low curing velocity at room temperature taking an undesirably long time for complete curing as well as in the poor mechanical properties of the cured products thereof such as fragility.